Olanexidine is a compound with high bactericidal activity having the chemical name 1-(3,4-dichlorobenzyl)-5-octylbiguanide. Research has been carried out into bactericides containing, olanexidine hydrochloride as an active ingredient (see Japanese Patent No. 2662343, etc.).
Olanexidine has very poor solubility in water, and hitherto known salts of olanexidine are also poorly soluble in water. For example, the solubility at 0° C. of olanexidine hydrochloride in water has been measured to be less than 0.05% (W/V), and the solubility of free olanexidine is a further order of magnitude less than this. Consequently, sufficient bactericidal activity cannot be expected of an aqueous solution merely having olanexidine dissolved therein, and moreover, depending on the conditions the olanexidine may precipitate out.
In the case of making an aqueous preparation of olanexidine in particular, to make the concentration of the olanexidine sufficient for exhibiting effective bactericidal activity, and to reduce the possibility of the olanexidine precipitating out, it has thus been considered necessary to use a dissolution aid such as a surfactant.